DE2234723A1 - PLASTIC RESIN MOLDING UNDER REDUCED PRESSURE - Google Patents

Description

DR. ING. E. HOFFMANN _ν · DIPL ·. ING. W. EITtE - JDH. DEER. NAT. K. HOFFMANN

D-8000 MDNCHENSI ARABELLASTRASSE 4 TELEPHONE (0811) 911087

kabushiki kaisha ,,

Tokyo / JAPAE

Pouring synthetic resins under reduced

pressure

The present invention relates to a method and a Device for pouring synthetic resins in the form of liquids under reduced pressure and even at room temperature,

So far it has been customary to use synthetic resins in the form of liquids, for example epoxy or polyester resins for solidification to cast in the required shape in predetermined molds, which is called "casting" and also such resins in to transfer the solid state in which they hermetically enclose articles of different shapes. The latter measure can be "potting", "encapsulation" or "sealing" to be named. In the area of the electronic parts producing Industry these measures are given the machinability

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and mass productivity encountered many problems. Recently, there has become known a technique for manufacturing electronic elements hermetically sealed with synthetic resins using transfer molding at reduced pressures or in vacuums. Compression molding is certainly advantageous in that it requires lower compression pressures than injection molding and compression molding, although the execution still requires pressures of 10 to 100 kg / cm at a temperature above 160 ° C. This has led to the disadvantage that the processed electronic parts can be damaged or impaired in their characteristics or characteristics as a result of the pressure and temperature just mentioned. In particular, it is noted that there are known a variety of electronic parts and elements which cannot withstand a casting temperature of 160 ° C. For example, piezoelectric elements of Rochelle salt having a melting point of 55 ⁰ C and a maximum temperature of 45 ° C and in addition are deliquescent and efflorescent. Accordingly, it will be understood that transfer molding cannot be used to hermetically encapsulate such piezoelectric elements with synthetic resins.

In addition, a variety of electronic parts and elements have recently been developed, leading to the advent of electric parts and has resulted in elements with better properties and smaller size than those previously produced. Some of those developed Parts and elements have not only proven unable to reduce these injection pressures used in transfer molding Withstand pressure, but put a complete encapsulation with synthetic resins using the known ones described above Spray techniques counteract difficulties. Namely, it has proven difficult to use synthetic resins in the form of liquids evenly in slots or holes of the order of 0.1 to 0.05 mm, which are present in electrical parts and elements can pour or inject.

Accordingly, the present invention has the task of

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a new and improved method and apparatus for potting synthetic resins in the form of liquids reduced Djnick available even at room temperature

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in particular for the hermetic containment of small-sized ones against physical and / or chemical damage sensitive electronic parts and elements suitable, with the machinability, mass productivity and conservation the properties of the product are marked.

The invention achieves the object by providing a method for pouring a synthetic resin in the form of a liquid for hermetically sealing workpieces, which comprises the steps placing the workpieces in place within, the cavities of the mold, one for each cavity, and pouring a liquid Mixture of a synthetic resin and a curing agent for this purpose in predetermined proportions at room temperature in the Mold cavities for enclosing the pieces in each of the cavities in the solid state and characterized in that · the mold is subjected to a predetermined reduced pressure and the liquid mixture of synthetic resin and curing agent into the Mold cavities sucked under reduced pressure at room temperature to completely fill the cavities and then the mold is returned to ambient pressure to solidify those parts of the mixture filling the cavities.

The shape can preferably be produced from plastic, which can easily be dissolved by the synthetic resin in the solid state.

A preferred device for carrying out the invention Process can be a vessel in which-an amount of a liquid mixture a synthetic resin and a curing agent therefor in a predetermined proportion and included at room temperature is, a container, with reducible pressure, a form, in whose cavities are arranged to be enveloped workpieces and which is detachably attached in the container, a normally closed

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senes electromagnetic valve, whereby the crucible with the Form is connected, a vacuum pump for evacuating the container, another, between the vacuum pump and the container attached electromagnetic valve, in the the first working position the container is effectively connected to the vacuum pump and the second working position the container is in communication with the ambient air, a pressure tester for measuring a predetermined reduced pressure inside the receptacle to open the first electromagnetic valve, thereby causing the liquid mixture is sucked from the crucible into the cavities of the mold, and on the complete filling of the cavities of the mold liquid reactive devices for closing the first electromagnetic valve while the vacuum pump is in operation stopped and the second electromagnetic valve is moved from its first to the second working position, to bring the pressure in the container back to ambient pressure.

To determine when the liquid mixture of synthetic resin and curing agent completely fills the cavities of the mold, you can the latter advantageously with corresponding outlet openings which open towards the outer surface of the mold and a shut-off device, for example a limit switch, which a selected outlet opening within of the container is attached adjacent to the overflow of the liquid mixture from the mold through the selected Outlet opening to respond by closing the first electromagnetic valve, while the vacuum pump is stopped and the second electromagnetic valve is brought from its first to the second working position.

The present invention is detailed by the following Description illustrated in conjunction with the accompanying drawings.

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Figure 1 shows a perspective view of a, reduced pressure casting device with a crawled one Figure 12 is a portion constructed in accordance with the teachings of the invention;

Figure 2 shows a longitudinal sectional view of a part of the device shown in Fig. 1 along the line II-II of Fig. 1, with the connected components in elevation are illustrated;

Figure j5 shows a perspective view of a Glasses in which a hearing is introduced and the one encapsulated Amplifier unit produced by the device shown in Fig. 1 with a portion cut away, to show, on an enlarged scale, the manner in which the encapsulated unit is arranged within the eyeglasses;

.Figure 4 is a perspective view of the reinforcement unit shown in FIG. 3 before it is connected to a Resin is encapsulated;

FIG. 5 shows a view similar to FIG. 4, but showing the amplifier unit after encapsulation shows; ■

, Figure 6 is a partial plan view of a a mold suitable for casting the amplifier units shown in Fig. 4, with a portion broken away, around the assembly to illustrate the mold cavities;

FIG. 7 shows a partial sectional view along the line VII-VII of FIG.

FIG. 8 is a perspective view of a bimorph piezoelectric element made from Rochelle salt; to which the invention is effectively applied;

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FIG. 9 shows a cross-sectional view of the element of FIG. 9, which is in an intermediate step of the Casting method according to the invention is shown;

Figure Io represents a view similar to Figure 6, however, Fig. 11 illustrates a shape suitable for casting elements such as those shown in Fig. 8; and

FIG. 11 shows a fragmentary cross-sectional view of the shape shown in FIG. 10 along the line XI-. XI the Fig. Lo.

Referring now to the drawings, it will be seen particularly in Figure 1 that an arrangement described herein includes a machine box Io and a receptacle 12 in the form of a rectangular box mounted on the machine box Io. As can be seen from Fig. 1, the container 12 is open at its top and is to close with a Cover plate 14 is provided, in which a transparent glass plate 16 is preferably embedded with the aim of the interior of the Container 12 to be observed. The glass plate, 16 is also required to withstand a directed external pressure to the container during operation under reduced Maintain pressure or vacuum. The cover plate 14 is shown in FIG. 2 shown as a closure of the upper side of the container 12 with an intermediate seal 18, thereby ensuring is that the container 12 is kept under reduced pressure or vacuum.

As best shown in Fig. 2, a mold 2o is detachably mounted within the container 12 and has a plurality of mold cavities 22 in longitudinal, spaced, aligned relationship. At the bottom Part of it is a rail 24 to connect all of the mold cavities 22 and an outlet port 26 attached to each of the Mold cavities 22 is in communication and on the upper upper

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surface of the form 2o is open. The cavities 22 have a dimension and shape determined by the., to be encapsulated Workpieces is predetermined. A boundary scarf • ter 28 is, as shown in Fig. 2, on the inner wall surface of the receptacle 12 is attached directly above the outlet port 26 at the right end with an aim to be hereinafter is explained.

The mold 20 is preferably made of an inexpensive plastic material, which facilitates its mass production while helping to release the particular encapsulations therefrom. Examples of such material are polypropylene, polyethylene, polyvinyl chloride, silicone resins, etc. Furthermore, the mold preferably has a structure that is easy to assemble and disassemble. A pot 30 for containing a quantity of a resinous material in the form of a liquid to be poured is connected at the bottom to a pipe J2 which has a normally closed electromagnetic valve J54 mounted therein.

The tube 3> 2 is releasably sealed against the adjacent side wall of the container 12 and ends in a pouring nozzle J6 which is firmly fitted into a running rail 24 of the mold 20. The valve J> h is used to control the amount of resin material that is poured into the mold 2o. A combined weighing device and mixing device j58 is attached adjacent above the crucible 3> o for producing a liquid mixture of synthetic resin and a hardening agent for this in predetermined proportions at room temperature, and cooperates with a level controller (not shown) attached in the crucible j5o, uiii to supply the crucible 3o with the liquid mixture to maintain its substantially constant height within the crucible. The amount of curing agent is variable compared to the synthetic resin according to the particular purpose and the temperature of the liquid mixture can be slightly above room temperature in order to achieve the optimum viscosity for

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to get the pouring,

The combined weighing and mixing unit and the level controller are known and do not form part of the invention, so that they do not need to be described further.

To the container that is hermetically sealed with the cover plate 14 12 to evacuate is a device to achieve a reduced pressure or vacuum, for example a vacuum pump 4o, connected by a tube to the interior of the container 12 via an electromagnetic valve 4-2 of the three-way cock type » The valve 42 has a first working position, the container 12 being effectively connected to the vacuum pump and a second working position in which the container with an air supply tube 44 communicates. Is the air supply tube 44 in communication with the interior of the container 12 via the valve 42, the container 12 is brought back to ambient pressure, after which the cover plate 14 automatically moves into the position shown in Fig. open position shown can be moved by means of a suitable device (not shown).

As can be seen from Fig. I, the vacuum pump 4o is suitably mounted inside the machine box Io and is operated by an electric motor 46 which is also located inside the same box. On this side of the container 12, opposite the crucible J5 °, a U-shaped mercury manometer 48 is attached to the machine box Io in such a way that the open arm of the "U" is in connection with the interior of the container 12 for a pressure or height the vacuum within the container 12 to indicate. 1 also shows a pair of small blocks 5o and 52 which are attached to the closed arm of the U-shaped manometer 48. These. Place blocks. Pressure sensors, preferably of the optical type, including a light source and a phototransistor, which fall in -derii closed arm of .dazwischenliegenden including the mercury ■

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Opposite manometers 48, although they are not shown.

The pressure gauge 5o reacts to the transition of the outer parts' of the mercury column naeia of the connected (light) source opening the electromagnetic valve 34, while the Pressure gauge 52 on the transition of the outer »parts of the mercury column after the connected (light) source reacts while stopping the vacuum pump 4o in order to prevent ^ that the pressure is reduced too much in the container. The pressure measuring devices 50 and 52 are in their positions along the closed arm of the "ü" 48 for presetting the heights of the reduced pressure or vacuum within the container 12 controllable, wherein the valve 34 and the pump 4o open accordingly and be stopped accordingly. It is understood that the U-shaped mercury manometer 5 ° by any suitable Pressure gauge types can be replaced. The in-Fig. 1 shown Reference numeral 54 denotes an operation switch for opening and closing the connected electrical equipment (not shown) including the motor 4o.

In the arrangement shown in Fig. 2 it is assumed that (not shown) to be potted or encapsulated workpieces are placed within the mold cavities 22, one for each cavity, and that the crucible ^ o with a liquid mixture of predetermined amounts of one to be poured Synthetic resin and a curing agent for this purpose is filled at room temperature and the valves ^ 4 and 42 are closed and in a position in which the interior of the container 12 is connected to the vacuum pump 4o. The arrangement also assumes that the pressure gauges 50 and 52 are in their desired positions on the pressure gauge 48. In other words, the arrangement shown in Figures 1 and 2 is ready for casting operation.

Under assumed conditions, the Sehalter 54 is closed-

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sen, the operation of the motor 6 causes the vacuum pump 40 to evacuate the interior of the container 12. When: the inside of the container 12 reaches a predetermined reduced pressure or vacuum value, which corresponds to the position of the pressure gauge 50 along the closed arm of the U-shaped manometer 48, the electromagnetic valve "52 is opened by a control circuit (not shown) This allows the liquid mixture of synthetic resin and its hardening agent to be poured or sucked out of the crucible 30 through the tube 32, the open valve 34 and the nozzle 36 into the mold 20 until all cavities 22 of the mold 20 are completely filled with the liquid mixture is filled with encapsulation of the corresponding workpieces (not shown) introduced therein as described above.

At the end of the casting process, the excess mixture flows through the outlet openings 26 onto the outer surface of the mold 20. This is measured by the limit switch 28. The operation of the end switch 28 closes the valve 34 and brings the valve 42 into a position in which the interior of the container 12 communicates with the air supply tube 44, while at the same time the motor 46 and therefore pump 40 are stopped. Accordingly, the pressure in the interior of the container 12 increases gradually until it has reached ambient pressure. At this point in time, the cover plate 14 is automatically brought into its open position, as illustrated in FIG. 1. It is understood that the end switch (28) can be replaced by any suitable type of a phototransistor or an electromagnetic relay R _e.

The mold 20 is then removed from the container 12 and the nozzle 36 is closed. The mold 20 is in this state left until the synthetic resin within the mold cavities 22

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is consolidated. After that, the resulting cast or the encapsulated workpieces are ejected from the mold cavities 22 become, ■ · ■ -.-

tr

Then another set to be encapsulated. ate. Throw, -: stüeken introduced into the now empty form or a new form. The method described above is repeated with the form arranged in the container.12. During the Vergießvorgahgs the pressure in your container 12; .. fall is shown measuring device 52 along the pressure gauge 48 This enables the pressure gauge 52, the motor 46, such as upstream ■; a "predetermined value among _t, the pressure by the _{Position'des;} ■■ standing described.. to stop, thereby preventing.

The invention can be effectively applied to a large number of work pieces, in particular electronic parts. and elements that work with Synthetic resins to be coated are to be applied * Suitable Examples of synthetic resins are epoxy resins, polyurethanes, polyesters, ' Silicone resins, polysulfide synthetic resins, etc. Any of these resins may be in the form or suitably incorporated therein in a liquid state at room temperature be mixed with a suitable hardener. A liquid mixture produced in this way preferably has a viscosity of about 20,000 centipoise at room temperature.

In FIG. ² J-- glasses is shown a gain unit is introduced as a hearing aid in the side frame, in accordance with: the present invention is .ή- ·> poured into synthetic _resin,;. .

The glasses generally designated with the reference number 6q ..- contain a side frame 62, in this case as in FIG. 3 shows a links frame, - in which a potted or. Encapsulated reinforcement unit 64 is arranged and one.

_ 1 2 _

Ear insert 66, which is connected to the frame -62 and is acoustically connected to the reinforcement unit 64 through a flexible acoustic pipe 68.

As can be seen from Fig. 4, there are a number of electrical components 7o on a support plate 72 made of suitable electrical insulation material is arranged to form the main body of the reinforcement unit 64. The arrangement of FIG. 4 is then placed in a block 74 of suitable electrical insulation resin, as can be seen from Fig. 5, embedded before it is inserted into the glasses.

To complete the arrangement of FIG. 5, a casting mold shown in FIGS. 6 and 7 can preferably be used although the invention is not limited thereby or thereto. The generally designated by the reference number 2o Mold includes a top half 2oA, a bottom half 2oB, and a plurality of mold cavities 22 that are in alignment are arranged. In the example shown, the larger part of the cavities 22 is formed in the lower mold half 2oB in such a way that that the one set of the reinforcement components 7o and the like Support plate 72 attached in the lower half 2oB with the surface of the lower half being substantially flush with the surface of the support plate facing the reinforcement components. On the other hand, owns the upper mold half 2oA a shallow depression that each Cavity part of the lower half 2oB superimposed, with the exception of the recess for each end part of the support plate.

Further, a rail 24 is disposed on an edge portion of the lower mold half 20B and connected to a plurality of gates 24A, each of which communicates with an individual pair of adjacent cavities 22. The rail 24 is connected on one side to the connected casting nozzle, which is shown by the numeral ~ $ 6 in FIG. The cavities 22 are each provided with an outlet opening 20 which, after a casting

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spigot or riser 25 opens that runs along the top of the Form 2o (see Fig. 7) runs.

The reinforcement units 6o are firmly inserted into the cavity parts formed in the lower mold half 2oB and then the upper mold half 2o-A is placed over it and fastened to the lower half 2oB by fastening bolts 76 (only one of which is shown). The mold 2o assembled in this way is introduced into the container 12: in the manner described above in connection with FIG. 2 and is ready for the casting process.

It has been found that such a booster unit is preferably encapsulated with an epoxy resin ^{sold by the Chiba Company under the name "Araldite D" or n} CY2oo "A curing agent suitable for this resin is commercially available sold under the name "HY956" by the same company.

The resin was mixed with the curing agent in a mixing ratio thoroughly mixed from loo to l8 to form a liquid, which had a viscosity of 1,800 centipoise at 20 ° C.

The procedure described above in connection with Figures 1 and 2 was repeated with the resin-curing agent mixture thus prepared. The suction of the mixture in the mold was 2o gain units shown 5, were prepared under reduced pressure or a vacuum which 8o mm of mercury corresponded caused _s thereby in Fig..

The reinforcement unit 64 encapsulated in this way can be introduced into the side frame 62 of the glasses -6o together with other accessories which includes a miniature microphone and receiver. One of these accessories is a volume control device 76 and a switch 78 by the example in both sides of the encapsulated Unit 64 shown in FIG. At the free end of the

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Side frame 64 can also accommodate a battery (not shown). The invention now applies to bimorph piezoelectric Elements Made From Rochelle Salt Explained. It is known to require such elements to be completely isolated from the surrounding air, since the Rochelle salt, which forms such piezoelectric elements, dissolves and is efflorescent.

Rochelle salt bimorph piezoelectric elements are usually formed in a structure as shown in FIG. Specifically, a pair of piezoelectric pieces 8o with electrodes 82 (only one of which is shown) becomes a bimorph Structure 84 cemented together including a pair of rails 86 made of any suitable metal foil. It is found that the structure of the Pig. 8. no device for their location within the connected cavity, as shown in Fig. 2 by numeral 22, contains. To this objection To invalidate, the bimorph element 84 can effectively be completely covered with a formed plastic film, for example made of vinylidene chloride resin, and / aur the opposite Corners or edges that have the largest intermediate space are provided with projections for the arrangement. For example, element 84 shown in FIG. 9 is one such Contains film 88, provided with a pair of projections 9o * the outer parts of which are removed from the connected surfaces of the element by the distance "d".

In Figures Io and 11, in which like reference numerals correspond Referring to components of Figures 6 and 7, a mold 2o is having a plurality of aligned cavities 22, which are attached in the lower half 20B, the configuration and dimension of which are just sufficient to permit the Elements of FIG. 9 to be included. Accordingly, the element 84 of FIG. 9 can easily pass through the connected mold cavity 22 be centered so that the projections 9o abut against the lower opposite edges of the cavity 22. The above methods & ann. described in connection with Figures 1 and 2

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with the mold 22 into the piezoelectric elements 84, as in the Pig. Io and 11 are introduced by the use of the resin and curing agent identical to those described in connection with Figs. However, there were loo ge. parts by weight of the resin mixed with 20 parts by weight of the curing agent, and the suction of the reducing mixture into the mold was caused under reduced pressure of 40 mm of mercury. A timing device (not shown) without omitting the end turn switch 28 was used to determine the pouring time of 15 seconds. Valves ~ $ h and 42 were then operated manually to bring the container 12 back to ambient pressure. -. . .

It must be established that the limit switch or limit switch can be replaced by any cut-off device that responds to the overflow of the liquid mixture out of the mold through the outlet ports by operating the valves ^ 4 and 42 and stopping the motor 46 and thereby the vacuum pump 4o responds. As the above-described resin-hardener mixture has a vapor pressure of 1.5 x 10 ~ mm Hg at 20 ° C, the value just explained causes the reduced No physical changes in the elements to be encapsulated due to pressure or vacuum. Potting is also carried out at room temperature carried out to thereby prevent the Rochelle salt from being adversely affected. That's why the piezoelectric elements are completely encapsulated by the resin.

The invention has several advantages. For example, the potting at lower temperatures ", e.g. room temperature, as long as the resin-hardener mixture used in the liquid state "sufficient fluidity at such temperatures. Therefore, the invention is particularly useful for potting, encapsulating or sealing physically and / or chemically fragile or sensitive electrical

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SAD ORIGINAL

tronic parts and elements such as the above-described Rochelle salt piezoelectric elements. The invention enables mass production, excellent workability, and property retention of the product achieved.

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Claims (3)

P at e nt to claims flT) Method of casting a synthetic resin in Forrrr Viner liquid under reduced pressure to be hermetically sealed Workpieces, marked by the process stages in which workpieces are placed in cavities a plastic mold, one per cavity is introduced, evacuation of the atmosphere in which the mold is located, measurement of the predetermined pressure, whichever is lower than the ambient pressure is to introduce a liquid mixture of a synthetic resin and a curing agent therefor to effect at room temperature in the cavities of the mold, and measurement, so that when the liquid mixture enters the cavities of the Form completely fills both the introduction of the liquid mixture into the mold cavities and the evacuation of the atmosphere around the mold is stopped, bringing the mold back to ambient pressure while allowing the resin to solidify .. 2. Apparatus for casting a synthetic resin according to claim 1, characterized by a combination, one Crucible in which an amount of a liquid mixture of a synthetic resin and a curing agent therefor is enclosed at room temperature is, a container with reducible pressure, a form, in the cavities of which workpieces to be wrapped are arranged and are releasably attached to the container, a normally closed electromagnetic valve, whereby the crucible with the Cavities of the mold is connected, a vacuum pump for evacuating the container, another between the vacuum pump and Electromagnetic valve attached to the container, in the first working position of which the container is effective with the vacuum pump is connected and in the second working position the container is in communication with the ambient air, one with the container effectively connected pressure tester for measuring a pre- 308835/0135 - 18 - certain pressure, which is less than the ambient pressure inside the container, to the first-mentioned electromagnetic Open the valve, thereby causing the liquid mixture from the crucible to be introduced into the cavities of the mold and a closing device which reacts to the complete filling of the cavities of the mold with the liquid of the first electromagnetic valve while the vacuum pump is stopped and the second electromagnetic valve from its first is brought into the second working position in order to bring the pressure in the container back to the ambient pressure bring. 3. Apparatus for casting according to claim 2, characterized characterized in that the device which reacts to the complete filling of the mold cavities with the liquid Outlet openings in the mold for connecting the connected cavities of the mold with the outer surface of the Form are arranged and a shutdown device includes a selected outlet opening within the container is mounted adjacent to prevent the liquid mixture from overflowing from the mold through the preselected outlet opening respond by closing the first electromagnetic valve while the vacuum pump is stopped and the second electromagnetic Valve is brought from its first to the second working position. I098S5 / 013S